Optical Transport Networks such as those specified in the ITU-T G.709 recommendation are known, having a control plane to control nodes of such networks to reserve (set up) new paths by sending messages between the nodes to reserve resources at each node.
Classical RSVP (Resource reSerVation Protocol) [RFC2205] signaling protocol is a known protocol for messages sent between nodes to set up new paths. RSVP-TE (RSVP-Traffic Engineering) [RFC3209] extends RSVP in order to provide a way to establish Label Switched Paths (LSPs) in MPLS (Multi-Protocol Label Switching). To reserve a path, an RSVP-TE (Traffic Engineering) PATH message, in the form of a Generalized Label Request, is sent out from the first node (which acts as an ingress node) via intermediate nodes along the proposed path, to the last node (acting as an egress node). The egress node returns an RSVP-TE RESV message to the ingress node, back along the path to cause the nodes along the path to confirm the reservation of resources such as bandwidth on switch paths and ports, for the requested path, for traffic of a signal type specified in the message.
It is non reliable in the sense that it relies on other mechanisms if a message is lost. It can recover from message lost via RSVP refresh messages. For example, if the sole tear down message transmitted is lost, then resources will only be deallocated once the “cleanup timer” interval has passed.
RSVP-TE does not change the intrinsic RSVP unreliability described above.
GMPLS (Generalized MPLS) [RFC3945] generalized the concept of LSP. An LSP became regarded as meaning “any possible form of connection which someone is willing to control”. Again, GMPLS does not change the intrinsic RSVP unreliability aspect.
The concept of a distributed Control Plane architecture providing, among others, signaling functions to dynamically set up/tear down LSPs over an underlying data transport network, introduces flexibility in allocation of network resources. This leads to an optimized on-demand bandwidth usage, ensuring network efficiency and allowing for greater scalability of topology.
On the other hand, the lack of a centralized control plane entity able to “see” and control the whole network, requires that single NEs are able to exchange all the information needed to stay aligned with each other and to keep their view of the underlying data plane consistent and up to date.
A basic requirement to make this possible is that connectivity among nodes at the control plane layer is in place. In case of failures affecting connectivity among nodes, prompt recovery from possible misalignments that can arise is more difficult.